Vitamin D deficiency and systemic inflammation indices in diabetic foot infection: associations with infection severity and length of hospital stay

Abstract

To investigate the associations of vitamin D deficiency and hemogram-derived systemic inflammation indices with infection severity and length of hospital stay in patients hospitalized for diabetic foot infection. This single-center retrospective cohort study included 220 adult patients hospitalized for diabetic foot infection. Vitamin D deficiency was defined as serum 25-hydroxyvitamin D less than 20 ng/mL. Infection severity was classified according to IWGDF/IDSA criteria. Hemogram-derived inflammatory indices, including neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, systemic immune-inflammation index, and systemic inflammation response index, were calculated from admission blood counts. Group comparisons, correlation analyses, logistic regression, linear regression, and receiver operating characteristic analyses were performed. Of the 220 patients, 109 (49.5%) had vitamin D deficiency; infection was classified as mild in 103 (46.8%), moderate in 66 (30.0%), and severe in 51 (23.2%). Compared with patients without vitamin D deficiency, deficient patients had higher BMI (32.1 ± 3.4 vs. 29.9 ± 3.8, p < 0.001), HbA1c (9.1 ± 1.0 vs. 8.3 ± 0.9, p < 0.001), NLR [5.7 (4.3–7.3) vs. 3.6 (3.0–5.0), p < 0.001], and SII [1774.0 (1282.0–2499.0) vs. 1042.0 (812.5–1450.0), p < 0.001], as well as longer hospital stay [14.0 (12.0–17.0) vs. 10.0 (8.0–12.0) days, p < 0.001]. Severe infection was more frequent among patients with vitamin D deficiency (36.7% vs. 9.9%, p < 0.001). Across increasing infection-severity categories, 25(OH)D decreased from 22.1 ± 4.8 to 17.1 ± 4.2 ng/mL, whereas NLR increased from 3.3 (2.7–4.0) to 8.2 (6.9–9.1) (both p < 0.001). In the adjusted analyses, NLR (adjusted OR 3.06, 95% CI 2.09–4.48, p < 0.001) and albumin (adjusted OR 0.10, 95% CI 0.01–0.76, p = 0.026) were independently associated with severe infection, whereas vitamin D deficiency (β = 0.192, 95% CI 0.112–0.273, p < 0.001) and NLR (β = 0.052, 95% CI 0.036–0.068, p < 0.001) remained associated with longer hospital stay. Low admission 25(OH)D characterized a more adverse clinical profile and remained associated with longer hospital stay, whereas NLR and albumin were independently associated with severe infection. These hypothesis-generating findings suggest that patients with elevated admission NLR and hypoalbuminemia may warrant closer assessment for severe infection, while low 25(OH)D should be interpreted as a marker of overall vulnerability.